Calibration of a mass spectrometer

Abstract

Apparatus and method are provided for calibrating a mass spectrometer. The calibration hardware includes a relatively small, relatively low pressurized tank for containing calibration gas. The calibration gas tank is preferably located inside the same housing that contains the ion source assembly and the analyzing section of the mass spectrometer. Each of the calibration gas and sample gas, whose components are to be determined, communicates with its own associated valve. These two valves control the flow of a selected one of the sample gas and the calibration gas to the ion source assembly. The calibration gas valve has an extremely low leakage rate and can be controlled to permit the passage of very low flow rates of calibration gas, which can be of benefit in checking the linearity associated with the ion source assembly pressure. For each calibration procedure, very small amounts of calibration gas are utilized, in a range around 10 -5 STD cc. A related method for conditioning an electron multiplier device is also disclosed in which the gain of one or more selected channels thereof is modified so that the output signal strengths of the device are comparable in magnitude. Calibration of the mass spectrometer occurs frequently and automatically. In one emobodiment, the mass spectrometer calibration is a direct function of each mass spectrometer measurement. Consequently, improved accuracy and heightened sensitivity are achieved in the mass spectrometer, while reducing the use or loss of valuable calibration gas.

What is claimed is: 
     
       1. A method for automatically calibrating a mass spectrometer, comprising: providing a housing containing a mass spectrometer apparatus used for generating ions and analyzing the ions;   providing canister means for containing and supplying calibration gas to said mass spectrometer apparatus;   providing a calibration gas valve communicating with said mass spectrometer apparatus and said canister means;   providing means for processing information relating to one or more components of said calibration gas;   providing output line means connected between said calibration gas valve and said canister means;   opening said calibration gas valve;   controlling calibration gas to flow into said mass spectrometer apparatus from said calibration gas valve at a rate less than about 10 -2  STD cc/sec;   preventing the presence of sample gas in said output line means wherein gas flow in said output line means is substantially non-molecular whereby the formation of dead space in the mass spectrometer is reduced;   using said mass spectrometer apparatus to analyze ions of said calibration gas components;   processing information relating to said ions; and   calibrating the mass spectrometer apparatus using said processed information.   
     
     
       2. A method, as claimed in claim 1, wherein: said step of providing said canister means includes locating said canister means entirely within said housing.   
     
     
       3. A method, as claimed in claim 1, wherein: said step of providing canister means includes containng said calibration gas at low pressure relatively close to atmospheric pressure.   
     
     
       4. A method, as claimed in claim 1, further including: monitoring the breathing cycle of a patient;   inputting a sample gas from the patient to a sample gas valve;   opening said sample gas valve during at least portions of the expiration part of the breathing cycle of the patient.   
     
     
       5. A method, as claimed in claim 1, wherein: said step of allowing includes permitting said calibration gas to flow from said calibration gas valve at a rate between about 10 -4  -10 -8  STD cc/sec.   
     
     
       6. A method, as claimed in claim 1, wherein: said step of allowing includes providing calibration gas in an amount of about 10 -5  STD cc or less for one calibration of the mass spectrometer.   
     
     
       7. A method for calibrating a mass spectrometer, comprising: providing an electron multiplier device having at least a first channel, said first channel having associated with it a gain of a first magnitude;   conditioning said first channel wherein said first channel gain is changed from said first magnitude to a second magnitude wherein said conditioning step includes supplying current charge to said first channel to reach said second magnitude of gain and monitoring the change in gain of said first channel to determine when said second magnitude of gain is reached;   incorporating said electron multiplier device with a mass spectrometer apparatus including means for generating ions and means for analyzing said ions;   providing canister means for containing and supplying calibration gas;   providing a calibration gas valve communicating with said mass spectrometer apparatus and said canister means;   opening said calibration gas valve to permit calibration gas to be ionized and analyzed in said mass spectrometer apparatus;   processing information relating to said ionized calibration gas; and   calibrating the mass spectrometer apparatus using said processed information.   
     
     
       8. An apparatus for calibrating a mass spectrometer, comprising: a housing;   input means for carrying sample gas;   a sample gas valve contained within said housing and communicating with said input means for controlling the flow of the sample gas;   ion source means contained within said housing for generating ions from said sample gas;   analyzing means contained within said housing and communicating with said ion source means for controlling movement of the ions;   processing means communicating with said analyzing means for processing information related to the ions to determine the relative presence of gas components;   canister means for containing and supplying calibration gas, said canister means being located entirely within said housing;   a calibration gas valve contained within said housing and communicating with said canister means for controlling the flow of the calibration gas wherein calibration gas in an amount of about 10 -5  STD cc or less is provided for calibration or the mass spectrometer;   output line means connected between said canister means and said calibration gas valve wherein no sample gas is present in said output line means and wherein gas flow is non-molecular in said output line means so that no dead space is formed whereby wasted calibrated gas is avoided; and   supply line means contained within said housing for supplying a selected one of the sample gas and the calibration gas to said ion source means.   
     
     
       9. An apparatus, as claimed in claim 8, wherein: said processing means includes means for monitoring time between calibrations so that it can be determined whether or not a predetermined interval of time has passed from a previous calibration whereby, if such a predetermined interval of time has passed, another calibration of the mass spectrometer apparatus can be provided.   
     
     
       10. An apparatus, as claimed in claim 8, wherein: said processing means includes means for controlling the opening of said calibration gas valve to achieve flow rates in the range of about 10 -4  -10 -8  STD cc/sec.   
     
     
       11. An apparatus, as claimed in claim 8, wherein: said canister means contains calibration gas at low pressure and relatively close to atmospheric pressure.   
     
     
       12. An apparatus, as claimed in claim 8, wherein: said canister means includes a canister having a capacity of between about 5-8 cubic inches of calibration gas.   
     
     
       13. An apparatus, as claimed in claim 8, wherein: said canister means includes a tank containing calibration gas and said supply means includes a common line communicating with both said calibration gas valve and said sample gas valve, said common line terminating at said ion source means, and wherein each of said calibration gas valve, said sample gas valve, said tank, said output line means, and said common line is contained within said housing.   
     
     
       14. An apparatus for calibrating a mass spectrometer, comprising: input means for carrying sample gas;   a sample gas valve communicating with said input means for controlling the flow of the sample gas;   ion source means communicating with the sample gas for generating ions using the sample gas;   analyzing means communicating with said ion source means for controlling movement of said ions;   processing means communicating with said analyzing means for processing information related to said ions to determine the relative presence of gas components;   a source of calibration gas;   a calibration gas valve communicating with said source of calibration gas for controlling the flow of the calibration gas wherein said calibration gas valve permits calibration gas to flow therefrom at a rate less than about 10 -2  STD cc/sec;   output line means connected between said calibration gas valve and said source of calibration gas wherein no sample gas is present in said output line means and wherein gas flow in said output line means is non-molecular whereby the formation of dead space in the mass spectrometer is reduced; and   supply line means contained within said housing for supplying a selected one of the sample gas and the calibration gas to said ion source means.